Hydrostabilizer



July 12, 1966 D. w. DOUGLAS 3,260,232

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HYDROSTABILIZER Filed Sept. 28, 1964 5 Sheets-Sheet 5 I NVE N TOR. Han/4m Wawzf United States Patent 3,260,232 HYDROSTABILIZER Donald W. Douglas, Rolling Hills, Calif., assigner to Douglas Aircraft Company, Ine., Santa Monica, Calif. Filed Sept. 28, 1964, Ser. No. 399,609 20 Claims. (Cl. 114-126) My present invention relates generally to stabilizers for stabilizing boats, seaplancs, and other similar craft. More particularly, it relates to a hydrostabilizer for effectively damping and suppressing the rolling motions of, for example, a boat which may be at anchor, drifting, trolling or cruising in a high and heavy sea.

Various devices have been used on boats and ships to damp and suppress the undesirable rolling motions resulting from a rough sea. These devices include, for example, cone shaped pans or buckets suspended from the sides of a boat into the water, fixed or activated fins mounted to the hull of a boat usually below the water line thereof, and submersible hydrofoils adapted to be suspended from the ends of respective poles or booms ex-tending out from opposite sides of a boat such that the hydrofoils are submerged in the water at a distance spaced away from the sides of the boat by the length of the poles or booms.

The suspended pans or buckets can act effectively to reduce and suppress roll of a boat when it is at anchor or drifting. They, however, cannot be used when the boat is under way because of the considerable drag produced by the submersed pans or buckets under such condition. The fixed or activated fins, on the other hand, are fairly effective in holding rolling of a boat down while it is under way but do not reduce or suppress rolling to any noticeable degree when the boat is drifting or at anchor in a heavy sea.

Activated fins installed on a boat are more effective than fixed fins in stabilizing the boat when under way because the activated fins can be continuously adjusted in attitude to provide suitable counteracting forces to oppose the undesirable motions of the boat. Such activated fin systems, however, are technically complex systems normally employing a rate gyroscope and are quite expensive. There is invariably a good deal of difficulty encountered in installing such systems in a finished boat. Considerable technical skill is required in adjusting an activated fin stabilizing system which also has high maintenance and operating costs.

The fixed or activated fins mounted to the bottom of a boat can also constitute a great danger to the boat. Apart from the possible damage done to such fins on striking a submerged object wherein some of the fins might be broken, there is always the greater danger that the bottom ofthe boat could be opened up, too. This might possibly occur, for example, when cruising at a relatively high speed in the open sea and then suddenly striking a large object such as a whale with the fins.

The suspended hydrofoil stabilizer system can obviate much of the diculties mentioned in connection with the suspended pan or bucket stabilizer systems and the fixed or activated fin stabilizer systems. A suspended hydrofoil stabilizer is, for example, shown, described and claimed in Patent No. 2,561,539, of Eugene R. Seward, on Submersible Marine Stabilizer for Boats, patented July 24, 1951. The submersible marine stabilizer disclosed in this patent comprises a substantially triangularly shaped stabilizer plate having a weight secured to the forward portion thereof, a stabilizer mast rigidly secured to a central, medial portion of the plate, and a fixed rudder member positioned to the rear of, and perpendicular to, the stabilizer plate. A single supporting wire connected to the upper end portion of the stabilizer mast is used to `suspend the marine stabilizer from the end of a pole or 3,25%,232 Patented July l2, 1966 boom extending from a side of a boat. Two such marine stabilizers are preferably used suspended from the ends of respective poles or booms extending from opposite sides of the boat.

The submersible marine stabilizer described above must necessarily operate in a prescribed manner in order to be effective. However, the configuration and structure of the marine stabilizer imposes certain stringent conditions under which it could effectively operate. For example, operating conditions which causes the attitude of .the marine stabilizer to be significantly altered as it is counteracting roll would render the device ineffective. Since only a single suspension wire is used and the marine stabilizer does not have any horizontal stabilizing n, the attitude of the device can easily change a significant amount during operation. In order to realize the advantages of a suspended hydrofoil stabilizer system, it is desirable that a new and useful suspended hydrofoil stabilizer system which operates well and is effective Ibe provided.

It is, accordingly, an object of my invention to provide a suspended hydrofoil stabilizer system for stabilizing a boat and the like, which is fully effective in operation while the boat is either at rest or under way.

Another object of this invention is to provide a stabilizer system for stabilizing a boat and the like, which can be safely used without undue concern of seriously damaging the boa-t in the event that the stabilizer system inadvertently strikes a submerged object.

A fur-ther object of the invention is 4to provide a suspended hydrofoil stabilizer system for stabilizing a boat and the like, which is stable in operation and maintains a correct operating attitude for effectively stabilizing the boat under all conditions of operation.

A still further object of the invention is to provide a stabilizer system for stabilizing a boat and the like, which is relatively inexpensive, has greater opera-ting effectiveness than comparable systems, not complex in structure, relatively small in size and light in weight, passive in operation and does not require a power source to operate, and can be easily adapted to be used on a wide variety of crafts of differing sizes.

Briefly, and in general terms, the foregoing and other objects are preferably accomplished by providing a suspended hydrofoil stabilizer system including a pair of hydrostabilizers which are each suspended on a pair of wires attached to spaced points along a line generally parallel to the longitudinal axis of lthe associated hydrostabilizer, the two pairs of wires being effectively connected to a boat and brought out along respective booms mounted to opposite sides of the boat preferably at its widest point, to suspend the hydrostabilizers from the ends of the booms into the water at points spaced away from the sides of the boat.

Each hydrostabilizer generally comprises a relatively long and thin body having a pair of hydrofoils accurately attached to opposite sides nea-r the forward end of the body, a tail or fin assembly including vertical and horizontal stabilizing Ifins attached to the aft end of the body, and a vertical mast secured near the forward end of the body. The mast has an upper, longitudinally elongate plate with end connections therein for attaching a pair of suspension wires. The center of gravity lof each hydrostabilizer preferably lies on its longitudinal axis, and the connection points of its suspension wires to the mast lie on Wire axes which, when extended, are located on respectively opposite sides of the center of gravity for proper operation of the suspended hydrostabilizer.

Another version of a suspended hydrofoil stabilizer system according to my invention includes a pair of hydr-ostabilizers which are each suspended on a set of three wires that are connected directly to the hydrofoil of their associated hydrostabilizer. The front wire of one set is effectively connected to a forward point `on the outer end of the associated boom extending from a side of a boat, and the remaining two rear wires are effectively connected to an aft point on the outer end of the boom, longitudinally spaced from the forward point.

Each hydrostabilizer of this latter version generally comprises a relatively long and thin body having a hydrofoil centrally and accurately secured to the forward end of the body, and a horizontal fin centrally and accurately secured to the aft end of the body. The hydrofoil is preferably a constant chord, straight leading and trailing edge hydrofoil which can be produced as an extrusion. The thin and elongated body of this hydrostabilizer furnishes all the directional stabilization required, and a vertical fin is not used at the tail of the device. The three suspension wires for the Idevice are preferably attached directly to points arranged in a triangular pattern on the hydrofoil such that a mast is not used or required.

My invention will be more fully understood, and other features and advantages thereof will become apparent, from the following detailed description of illustrative embodiments of the invention t be taken in conjunction with the accompanying drawings, in which:

FIGURE 1 is a frontal, head-on view of a boat equipped with a stabilizer system according to my invention;

FIGURE 2 is a perspective view of the starboard hydrostabilizer suspended from its boom which is mounted to the side of the boat shown in FIGURE 1;

FIGURE 3 is a side elevational view Iof the hydrostabilizer shown in FIGURE 2;

FIGURE 4 is a top plan view of the hydrostabilizer shown in FIGURE 3;

FIGURE 5 is a perspective view of the left hydrofoil of the hydrostabilizer `shown in FIGURES 3 and 4;

FIGURE 6 is a sectional view of the hydrofoil as taken along the line 6-6 indicated in FIGURE 5;

FIGURE 7 is a top plan view of another hydrostabilizer which differs in some respects from the hydrostabilizer shown in FIGURES 3 and 4;

FIGURE 8 is a side elevational view of the hydrostabilizer shown in FIGURE 7;

FIGURE 9 is a simplified drawing illustrating the correct operation of the hydrostabilizer during one phase of its operation;

FIGURE l() is another simplified drawing illustrating a condition of the hydrostabilizer to be prevented;

FIGURE ll is a perspective view of a simplified version of the hydrostabilizer;

FIGURE 12 is a top plan view of the simplified hydrostabilizer;

FIGURE 13 is a side elevational view of the simplified hydrostabilizer;

FIGURE 14 is a `sectional view of an attachment on the simplified hydrostabilizer as taken along the line -14- 14 indicated in FIGURE 13;

FIGURE 15 is a fragmentary, side elevational view of another attachment on the simplified hydrostabilizer; and

FIGURE 16 is a frontal view of the attachment as taken along the line 16-16 indicated in FIGURE l5.

FIGURE l is a frontal, head-on view of a boat 2() which is equipped with a stabilizer system 22 according to my invention, The boat mounts a pair of hydrostabilizers 24 and 26 which are effectively suspended from the ends of booms 28 and 30, respectively, such that they are fully submersed in a body of water 32. The hydrostabilizer 24 is suspended on a pair of wires 34 into the water 32 which is, for example, that of the ocean and, similarly, the hydrostabilizer 26 is suspended on another pair of cables or wires 36 into the water 32.

rIhe boat 20 is, illustratively, about 75 feet long and about 16 feet wide. The booms 28 and 30 are each approximately 10 feet long and are each rotatably mounted at about amidships to pivot in a vertical transverse plane from each side of the boat 20. The outer ends of the booms 28 and 30 are connected by respective ropes 38 and through suitable pulley systems to a common point 42 on mast 44. The ropes 38 and 40, together with their respectively associated pulley systems, are used to raise and lower the booms 28 and 30 pivotally between a substantially horizontal position and a substantially vertical one.

When the stabilizer system 22 is not being used, the booms 28 and 30 are normally raised to their vertical positions by the ropes 38 and 40 to reduce the necessary lateral clearance required for the boat 20. The hydrostabilizers 24 and 26 can be conveniently stowed by securing them to the undersides of the booms 28 and 30, respectively. Brackets (not shown) attached to the undersides of the booms 28 and 30 Iare adapted to engage and secure the hydrostabilizers 24 and 26 in place; however, any suitable means can be used to fasten the hydrostabilizers 24 and 26 securely in place to the undersides of the booms 28 and 3f).

To place the stabilizer system 22 in use, the hydrostabilizers 24 and 26 are released from the undersides of the booms 28 and 30 which are then pivotably lowered by the ropes 38 and 40 to the positions generally shown in FIGURE 1. The ropes 38 and 4() each make an angle of roughly to 55 degrees with their respectively associated booms 28 and 30, and the pairs of wires 34 and 36 as measured from the ends of the booms 28 and 30 extend downwards into the water 32 for a distance of approximately 9 feet, for example. The stabilizer system 22 is effective in stabilizing the boat 20 and suppresses the undesirable and disruptive, sudden roll movements thereof while at anchor, drifting, trolling or cruising.

The booms 28 and 30 are rotatably mounted to the sides of the boat 20 preferably at its widest point. This can be at about midships or it can be nearer the stern if the boat 20 has a squared stern. In the latter instance, the booms 28 and 30 are rotatably mounted to the sides at a point which is, for example, about one-fourth of y20 degrees/5 seconds or 4 degrees per second.

the length of the boat 10 forward of the stern.

In normal operation, regular rolling characteristics are experienced by the boat 20 in which the rolling motion has a period of 5 or 6 seconds. For a boat speed 0f, for example, 91/2 knots or 16 feet per second, the boat 28 may illustratively roll l0 degrees from side to side or a total of 20 degrees over a full cycle. A boat will usually roll isochronously; that is, the period or time of one complete roll is the same for all roll amplitudes. A roll deviation to either side of a normal vertical is indicated by the angles A and B in FIGURE l.

For a period of, for example, 5 seconds and a complete roll of 20 degrees (angles A and B each equal to 5 degrees), the boat 20 then rolls at an average rate of If the complete roll is l0 degrees, then the boat 20 pulls at an average rate of 10 degrees/5 seconds or 2 degrees per second. The hydrostabilizers 24 and 26 are suspended approximately vertically from the ends of the booms 28 and 30. Since the boat 20 is about l6 feet wide and th'e booms 28 and 30 are each approximately 10 feet long, the hydrostabilizers 24 and 26 are connected through the pairs of wires 34 and 36 to respective moment arms which extend approximately 18 feet in opposite directions from the vertical, central longitudinal plane including the center of gravity of the boat 20. Reaction forces of the water 32 loading the hydrostabilizers 24 and 26 due to any rolling motion of the boat 20 produce moments which tend to stabilize the boat 20 and will moderate the undesirable, sudden and disruptive characteristics of the rolling motion.

FIGURE 2 is a perspective view showing the hydrostabilizer 24 suspended from the end of the boom 28 on the pair of Wires 34. Wire 34a is connected on one end to the hydrostabilizer 24, passed over a pulley 46a mounted at the outer end of the boom 28, and follows the boom 28 back to a re'el 48a to which the other end of the wire 34a is attached. Similarly, wire 34b is connected on one end to the hydrostabilizer 24, passed over another pulley 46b mounted at the outer end of the boom 28 at a point spaced longitudinal-ly apart from the pulley 46a, and generally parallels the wire 34a back to reel 481) to which the other end of th'e wire 34b is attached. The pair of reels 48 are rotatably mounted on a board 50 which is secured to the boom 28 near the starboard side of the boat 20. However, since the boom 28 is attached to the starboard side of the boat 20, the reels 48 are also effectively attached thereto.

The pair of pulleys 46 are positioned at the outer end of the boom 28 such that the v'ertical portions of the wires 34a and 34b lie in a vertical plane which is generally parallel with the vertical plane including the central longitudinal (keel) axis of the boat 2t). The reels 48a and 48b have respective cranks 52a and 52h which can be turned to raise or lower the hydrostabilizer 24. The wires 34a and 34h can be suitably marked along their lengths with indicia 54 to indicate the lengths of wire that have been unreeled from each of the reels 48a and 48h. The pitch of the hydrostabilizer 24 can, of course, be adjusted by varying the relative lengths of the wires 34a and 34h that are unreeled from the reels 48a and 48b, respectively.

While a pair of reels 48 are used to control the pair of wires 34, the pair of reels 48 can be replaced by a single reel having a single crank by proper routing of the wires 34a and 341) to wind lcorrectly around the single reel. Such routing can be accomplished, for example, by appropriate positioning and use of suitable guide rollers (not shown) which can be adjusted in position to vary the relative vertical positions of the ends of the wires 34a and 34b connected to the hydrostabilizer 24 so that its pitch can be adjusted. The indicia 54 can also be deleted from the wires if the reels 48a and 48b are provided with indicators (not shown) which are vcalibrated to indicate the lengths of wire that have been respectively unreeled from the reels 48a and 48b.

The boom 28, as shown in FIGURE 2, can be in the form of an A frame having its inner ends 56a and 561!) rotatably secured to respective brackets 58a and 58b which are mounted to railing 68 on the starboard side of the boat 20. The outer end 62 of the A frame has a flange 64 which is connected to plunger 66 of a hydraulic cylinder 68 that is, in turn, connected to pulley 70 and the rope 38. A hose 72 connects the cylinder 68 to indicator 74 through a control valve 76. The connected cylinder `68 and indicator 74 comprise a dynamometer which can be used to measure the anti-rolling load produced by the hydrostabilizer 24 submersed in the water 32. The dynamometer is used for test purposes, and is preferably deleted under normal conditions.

The above description of the hydrostabilizer 24 and its mounting system as shown in FIGURE 2 is, of course, fully applicable to the hydrostabilizer 26 and its mounting system on the opposite, port side of the boat 20. While only a single hydrostabilizer could be used on either side of the boat 29 to stabilize the same, a pair of hydrostabilizers on opposite sides of the boat 20 is preferably used for greater effectiveness. If only a single hydrostabilizer were used on one side of the boat 20, anti-roll forces will be produced only when the boat 20 rolls in a direction opposite to the side on which the single hydrostabilizer is mounted. However, the tendency to roll even with a single hydrostabilizer is significantly opposed for a major portion of each cycle and roll is considerably moderated when averaged over a number of cycles.

The hydrostabilizer 24 has a body 78 to which is attached a pair of hydrofoils 80 near the forward end of the body 78, Stabilizing tins 82 including a vertical iin (82a) and two horizontal fins (82b and 820) are attached to the aft end of the body 78 as illustrated. A vertical mast 84 is provided near the forward end of the body 78,

and the wires 34a and 34b are attached to the upper portion thereof near its longitudinal ends to supportthe hydrostabilizer 24. The other hydrostabilizer 26 mounted on the port side of the boat 20 is, of course, preferably similar to the hydrostabilizer 24 shown in FIGURE 2.

FIGURES 3, 4, and 5, together, illustrate full construction details of an exemplary embodiment of my invention. A side elevational view of the hydrostabilizer 24 is shown in FIGURE 3, a top plan view thereof is shown in FIG- URE 4, and a perspective view of the left hydrofoil a is shown in FIGURE 5. Generally, the hydrostabilizer 24 has a shape resembling an airplane and is symmetrical about a central, longitudinal, vertical plane. The hydrostabilizer 24 is, for example, about 40 inches long having an end-to-end span of the hydrofoils 80a and 80b of approximately 641/2 inches.

The body 78 is preferably made of wood such as mahogany and is, for example, about 271/2 inches long, 51/2 inches wide at its widest point, and 11/2 inches thick throughout most of its length. The upper surface 86 of the body 78 slopes gradually from its maximum width of 5 1A. inches down to a width of about 23/4 inches at the tin end of the body 78 as shown in FIGURE 3. The lower surface 88 of the body 78 is substantially level or horizontal with a central, longitudinal, horizontal plane through the longitudinal axis of the body 78. As can be seen in FIGURE 4, the sides of the aft end of the body 78 are also gradually tapered inwardly beginning at about the leading edges of the horizontal ns 82b and 82C from its thickness of l`1/2 inchesl to about 1/2 inch at the aft edge of the body 78. This, of course, fairs-in the aft end portion of the body 78 with the vertical fin 82a to reduce drag.

The vertical fin 82a is, for example, an aluminum alloy sheet which is approximately 9/16 inch thick, 4l/2 inches wide, and 1401/2 inches long. The vertical iin 82a is preferably welded to another aluminum alloy sheet which is, for example, 3/16 inch thick, 41/2 inches wide, and 20 inches long such that the vertical iin 82a is centrally affixed to the other aluminum alloy sheet to form the two horizontal tins 82b and 82C therefrom. The lower surface of the vertical lin 82a is longitudinally slanted so that the lower leading edges of the horizontal fins 82b and 82C are set at the same level as the upper trailing edges thereof.

The aft end of the body 78 has a central vertical slot 90 longitudinally cut therein and `a transverse groove 92 which is angled upwardly at its forward end cut in the lower surface 88 of the body 78. Thus, when the Welded ns 82 are assembled to the aft end of the body 78 with the vertical iin 82a in the slot 90 and the adjacent portions of the horizontal lins 82b and 82C positioned in the angled groove 92, the lower leading edges and the upper trailing edges of the horizontal tins are level with the lower surface 88 such that a positive, horizontal 1in setting angle C is obtained. The fins 82 are secured in place by rivets 94. The angle C is, for example, 3 degrees.

The hydrofoils 80a and 80b are preferably aluminum castings each having a blade portion and a base portion. The hydrofoil 80a is illustrated in FIGURE 5 and the other hydrofoil 80b is, of course, similar thereto. The base 96 has a generally constant flange thickness except for a portion at the trailing end which is cut out in a step, leaving a uniformly thinner ange portion 98. Holes 100 are provided in this flange portion 98 so that the hydrofoil 80a and the similar hydrofoil 80b can be secured to the forward end of the body 78 by screws 102 as shown in FIGURES 3 and 4. The holes 100 are shaped to receive the heads of the screws 102. The ends of the screws 102 pass through corresponding holes in the forward end of the body 78 and engage suitably tapped holes in the base of the hydrofoil 80b corresponding to the holes 100.

Other holes 104 and 106 are similarly provided in the -base 96 as indicated in FIGURE 5. Holes corresponding to the holes 104 are provided in the lower end portion of the upright column plate 108 of the mast 44 shown in FIGURE 3. The lower end portion of the column plate 108 is .sandwiched between the bases of the two hydrofoils 80a and 8017 and secured thereto by screws 110. A ller plate 112 indicated in FIGURE 4 is `also sandwiched between the bases of the hydrofoils 80a and 80b in the longitudinal space between the trailing end surface of the column plate 108 and the forward end surface of the body 78. Screws 114 are used in the holes 106 and corresponding holes in the liller plate 112 and base of the hydrofoil 80b to secure the plate 112 and .adjacent portions of the bases of the hydrofoils 80a and 80b together as shown in FIGURE 3. The remaining gap between the bases of the hydrofoils 80a and 80b before the forward end surface of the column plate 108 is preferably plugged with a mahogany strip 116 that is cemented in place therein.

The bases of the hydrofoils 80a and 80h are, for example, approximately 151/2 inches long, 51/2 inches Wide, and 3A inch thick except for the thinner flange portion 98 which is 1A inch thick. The column plate 108 is, illustratively, 14% inches long (or high), 6 inches wide, and 1/2 inch thick. Similarly, the filler plate 112 is 51/2 inches square and 1/2 inch thick. The mast 44 has a longitudinally elongate plate 118 which is 151A inches long, 2% inches wide and lz inch thick, and shaped as shown in FIGURE 3, welded orl otherwise allxed to the upper end surface of the column plate 108. Two holes 12011 and 120b which are, for example, spaced 14 inches apart, are located near respective ends of the elongate plate 118. These holes 120a and 120b lie on a line which is generally parallel to the longitudinal axis 122 of the hydrostabilizer 24 and located at a distance of approximately 14 inches above such axis 122.

The weight of the hydrostabilizer 24 in air is 128 pounds and its weight in water is 74 pounds, for example. The center of gravity of the hydrostabilizer 24 is located on its longitudinal axis 122 at a point indicated by the vertical line 124 which intersects the line joining the centers of the holes 1200 and 120b at an intermediate point |between the centers of these holes. The ends of the wires 34a and 34b are connected to the respective holes 120a and 120b as shown in FIGURE 2. The mast 44 thus raises the connection points at which the ends of the wires 34a and 34b are attached and provides connection holes 120a and 120b which are spaced signicantly apart longitudinally on opposite sides of the vertical direction of the center of gravity. This reduces the tendency of the hydrostabilizer 24 to yaw; i.e., to twist on the connecting wires 34a and 34h, and the pitch of the hydrostabilizer 24 can be also closely cont-rolled and prevented from changing or varying to any significant extent.

When the hydrofoils 80a and 801b are properly assembled to the body 78, they both have an angle of incidence D (horizontal hydrofoil setting angle) which is negative as indicated in FIGURE 3. This angle of incidence D is, for example, -5 degrees. The planform of the hydro-foils 80a and 80b has a high aspect ratio, with sweepback and a constant taper ratio. The planform has a straight 100% (trailing edge) line as lcan Ibe seen in FIGURE 4. The root section of the hydrofoil 80a shown in FIGURE 5. is similar to its tip section. A line 126 of maximum section thickness and another line 128 joining the two end sections are indicated in FIGURE 5. These lines 126 and 128 are located at respective distances of .3 and .6 of chord length from prole leading edge, and a straight taper is followed along these lines. The relative thickness and shape of the hydrofoil sections are maintained substantially constant.

FIGURE 6 is a sectional view of the hydrofoil 80a as taken along the line 6-6 indicated in FIGURE 5. The hydrofoil section 130 is observed to be substantially symmetrical and is typical of any section taken along the span of the hydrofoils 80a and 80b. For a relative velocity v indicated in FIGURE 6 due to operation of the hydrostabilizer 24 as shown in FIGURE 2, the hydrofoils a and 80h normally have a negative angle of attack E. This angle of attack E will 'be initially equal to the angle of incidence D of, for example, -5 degrees and increases to larger angles of attack with increasing angular roll velocity of the boat 10. The angle of attack E increases because of the addition of a vertical cornponent of velocity introduced in the relative water flow over the hydrofoils 80a and 80b by their upward motion due to roll of the boat 10.

The hydrostabilizers 24 and 26 each maintains its proper attitude and stays at a fairly regular angle of attack E with motion of the boat 20. There is only a small movement of the center of pressure of the hydrofoils during use. Drag increases with increasing angle of attack, of course, and the hydrostabilizer stalls at about 20 degrees. The anti-roll damping force is produced on the negative sides ofthe hydrofoils which have an effective area of about 51/3 square feet for each hydrostabilizer. The dynamometer indicator 74 in FIGURE 2 has measured loads on the hydrostabilizer 24 which were at times as high as 2100 pounds that is taken by the hydrofoils 80a and 80h. Since the moment arms extend approximately 18 feet in opposite directions from the vertical, central longitudinal plane including the center of gravity of the boat 20, the roll of the boat 20 is suppressed and damped by a very substantial moment equal to the load on the hydrostabilizer multiplied by the length of its moment arm.

The boat 20, however, must roll before a counteracting force or load is produced on the hydrostabilizers by the water 32. In this regard, it is to be noted that in any significan-t heavy sea, the anti-rolling load on the windward hydrostabilizer is quite larger than that on the leeward hydrostabilizer. This is caused by the heaving of the boat 20. Since small boats encounter more heave in proportion to their size than do the large vessels normally, the hydrostabilizer systern 22 is particularly effective and benecial to the smaller boats which may be subjected to unacceptable rolling motions in a very high and heavy sea. Fixed or controlled stabilizing ns, for example, which are mounted to the hull below the water line, and particularly if they are vertical or nearly vertical tins, will not gain as much counteracting forces from heave as do my hydrostabilizers.

FIGURES 7 and 8 show another hydrostabilizer 132 which differs in some respects from the hydrostabilizer 24 illustrated in FIGURES 3 and 4. The hydrostabilizer 132 has a body 134 to which are secured hydrofoils 136a and 136b, and a tail or iin assembly 138. The body 134 has a nose 134a which is preferably made of lead, a forward body portion 134b preferably made of dural, and an aft body portion 134e preferably made of wood. A support bracket 140 has vertical legs 140a and 140b attached to respective studs 142a and 142b in the forward body portion 134k so that the legs 140a and 14011 are attached to points which are respectively located forward and aft of the longitudinal position of the center of gravi-ty of the hydrostabilizer 132, indicated by the vertical arrow 144. The center of gravity of the hydrostabilizer 132 in water and the center of pressure of the hydrofoils 136a and 13611 are at the position indicated by the arrow 144 located on the longitudinal axis 146.

Suspension cables or wires 148a and 148b (FIGURE 8) are connected to transverse pins 150g and 150b, re-` spectively, which are positioned in the channel of tie bar 140C (FIGURE 7) directly above the vertical axes of the legs 140a and 140b. The Wires 1485i and 14811 have not been shown in FIGURE 7 for clarity of illustration but these wires 143a and 148b correspond respectively to the wires 34a and 34h of FIGURE 2, and are used to suspend :the hydrostabilizer 132 from the end of a boom such as the boom 28. The hydrostabilizer 132 is about 5 feet long and has a hydrofoil planform endto-end span of approximately 651/2 inches. The weight ofthe hydrostabilizer 132 in air is about 150 pounds and its weight in water is about 106 pounds.

The hydrofoils 136:1 and 136i) are preferably aluminum castings and are similar to the hydrofoils 80a and 80h shown in FIGURES 3, 4 and 5. In fac-t, the main dif ference is in the shape of the base portion 152 as can be seen in FIGURE 8 as compared with the base portion 96 shown in FIGURE 3. The hydrofoils 88a and 8911 are accurately secured to the forward body portion 13411 by screws 154 as indicated in FIGURE 8 such that the hydrofoils have a negative angle of incidence F. This angle of incidence F is, for example, -5 degrees as in the hydrostabilizer 24 described above. The planform of the assembled hydrofoils 136a and 136]; is, of course, similar to that of the assembled hydrofoils 80a and 88h on the hydrostabilizer 24. However, other forms of hydrofoil sections and other types of planforms can be utilized in a suitably designed hydrostabilizer without detriment to its elfectiveness.

The tail or n assembly 138 prevents hunting of the hydrostabilizer 132 during operation as do the fins 82 of the hydrostabilizer 24 shown in FIGURES 3 and 4. The fm assembly 138, however, includes four ns 156a, 156b, 156e and 156d secured in a cruciform arrangement as illustrated in FIGURES 7 and 8. The end-to-end span of the horizontal tins 156a and 156b is, for example, 22 inches and the end-to-end span of the vertical ns 156C and 156d is 17 inches. The ns 156 each have a sharpened leading edge which gradually tapers outwardly into the regular thickness of the at plate forming a fin. A fairing 158 shaped as indicated in FIGURES 7 and 8 can be suitably slotted to t on the fins 156 and secured theret0.

The 1in assembly 138 is -connected to the aft body portion 134e by a semicircularly curved extension portion 160 of the vertical tins 156C and 156:1 which extends into a vertical end slot 162 in the aft body portion 134C and is rotatably secured therein by a bolt and nut fastener 164. Bearing plates 166a and 166b are secured to the aft end on opposite sides of the body portion 134C by screws 168. The fastener 164 is supported by the bearing plates 166a and 166b so that the extension portion 160 and its attached fin assembly 138 can be rotated through a relatively small angle on the axis of the fastener 164.

The semicircularly curved extension portion 160 has a number of closely spaced holes 170 therein arranged in an arc. A screw 172 connecting two aligned holes in the respective bearing plates 166a and 1661), and passing through a selected one of the holes 170 will hold the horizontal fins 156a and 156b at a desired angle of incidence G indicated in FIGURE 8. For the illustrated hydrostabilizer 132, a negative angle of incidence G of, for example -3 degrees was found to be effective in supplying an appropriate stabilizing moment to augment proper operation of the hydrostabilizer 122.

In operation, if there is no forward motion and no rolling of the boat 20, the hydrostabilize1j132 (assumed suspended from boom 28 in FIGURE 1) is normally maintained substantially horizontal or level on its supporting wires 148a and 148b (FIGURE 8). When the boat 20 rolls, the relative direction of water ow is essentially in a vertical, downward direction while the hydrostabilizer 132 is rising. Since the hydrostabilizer 132 is suspended from the end of the boom 28 extending from the side of the boat 20, the greater the angular velocity of the roll of boat 20, the greater will be the relative vertical Velocity of the flow of` water. A greater force or load. is thus imposed on the hydrofoils 136g and 136b of hydrostabilizer 132 and this means that a greater roll damping moment is` produced to suppress the rolling of boat 20.

FIGURE 9 illustrates the correct operation of the hydrostabilizer 132 during that part of a roll when it is moving downwards where .there is no forward motion of the boat 20. The support bracket 140 (or the mast 44) lowers the center of gravity of the hydrostabilizer 132 relative to the wire attachment used on the hydrostabilizer 132 (or hydrostabilizer 24) but is not, of course, absolutely necessary and the Wires 14801 and 148b are shown connected directly to the body of the hydrostabilizer 132 for clarity of illustration. The purpose of the horizontal ns 156a and 15611 is to, cause the down moving hydrostabilizer 132 to dive during this interval. In order to do this, the horizontal ns 156a and 156b are made large enough such that the tail or horizontal 1in loadi174multiplied by the distance X substantially exceeds the weight 176 of the hydrostabilizer 132 multiplied by the distance Y. The tail moment about the front wire 148:1 support center 178 then overcomes the moment of the weight of the hydrostabilizer 132 about this center 178 and lifts the tail up, causing the rear wire 14811 to become slack and `the hydrostabilizer 132 to dive.

If the boat 20 is assumed to be now under way and there is no rolling of the boat 20, the hydrostabilizer 132 is normally maintained substantiallyhorizontal or level on its supporting wires 148aand 148b (FIGURES) such that the path of water flow with a relative velocity v is parallel to the longitudinal axis 146 of the hydrostabilizer 132. Thus, under these circumstances, the angle of attack (similar to angle E in FIGURE 6) is substantially equal to the angle of incidence F of thehydrostabilizer 132 shown in FIGURE 8. If there is no rolling of the boat 20 (with the hydrostabilizer 132 assumed suspended from boom 28) the angle of attack of the towed hydrostabilizer 132 would only vary with boat speed due to changes in structural deections of the hydrostabilizer 132. During a rolling condition, however, the angle of attack will vary, depending upon the angular velocity of the roll and the speed of the boat 20.

When the boat 20 rolls as it is under way, and pulls the hydrostabilizer 132 upwards on the up roll, there is produced a vertical, downward component of vel-ocity of relative water flow, which depends upon the angular velocity of the roll and the length of thevmoment or radius arm from the plane of symmetry ofthe boat 20 to the end of the boom 28. The greater the angular velocity of the roll, the larger this verticali velocity component becomes, of course. Since the vertical velocity component is introduced by rolling, the angle of attack which was originally equal to the (negative) angle of incidence F, will increase negatively to the resultant direction of relative water flow due to the combination of the forward and upward motions of the hydrostabilizer 132.

The angle of attack increases from the angle of incidence F of -5v degrees to, for example, about -20 degrees in a 20 degrees roll (40 degrees overall) at a 5 second rolling period and at a speedof 91/2 knots of the boat 20. This increase in angle of attack with increase of angular velocity of roll means that the faster is the roll, the greater becomes the load on the rising hydrostabilizer 132 and hence the greater becomes the roll damping moment on the boat 20. This action differs from the situation in which there was no forward motion of the boat 20 in that the. angle of attack was formerly established only by a substantially Vertical, downward velocity component of relative water ow.

When the boat 20 is under way and is rolling, the horizont-al fins 156a and 15619` are also designed to meet the following situation. Assume that the hydrostabilizer 132 is suspended from`4 the boom 28 on the right side of the boat 20 and has been rising as the boat 20 rolls to the left side. The hydrostabilizer 132 has been restrained by the two wire suspension system so that the setting or inclination of its hydrofoils 136a'and 136b in respect to the boat 20 remains at the set angle (usually approximately -5 degrees which is equal to the angle of in, cidence F for relative water flow parallel to the longitudinal axis 146 asiindicatedin FIGURE 8').

Due to the-roll of the boat 20fraising-this right side hydrostabilizer 132, the angle of the flow of water. over` the hydrofoils 136m andlb'has been more, thauthe points and is preferably -5 degrees set angle. That is, the angle of attack of the hydrofoils 136a and 136b is more than -5 degrees. Likewise, the angle of ow of the water over the horizontal tins 156a and 1561; has changed. Under this condition and at the maximum increase of angle of the down owing water (in relation to the hydrostabilizer 132), the horizontal tins 156a and 15611 must not produce forces or moments powerful enough to change the set angle of the hydrofoils 13611 and 136k, relative to the boat 20. If the forces of moments of the horizontal fins 156g and 15611 were to do this, it would decrease the angle of the water flow over the hydrofoils 136er and 13612 and hence reduce the total load thereon which is then needed to damp the roll.

Consider, now, the case where the right side hydrostabilizer 132 is sinking as the boat 28 is rolling to the right side. It is well-known that under many conditions, this down motion of the hydrostabilizer 132 will cause the angle of the relative flow of the water to become positive over the hydrofoils 136a and 13617. Since the hydrostabilizer 132 would ily and possibly surface if this were permitted to persist, the horizontal tins 156a and 156b must be designed to provide a load powerful enought to prevent this.

FIGURE illustrates the attitude of the hydrostabilizer 132 which is to be overcome and normally prevented by an appropriate horizontal iin load when the hydrostabilizer 132 is sinking as the boat 20 is rolling to the right side, for example. The area andthe angle of incidence (angular setting) of the horizontal tins 156a and 156b are designed to always keep a reasonable load 174 on the front support wire 148a under this condition so that the wire slackness indicated in FIGURE 10 would be prevented. This load 174 must not be greater than necessary, of course, since this load is working with and not against the roll of the boat 20.

The angle of incidence F indicated in FIGURE l0 is, for example, -5 degrees. The direction of the resultant water flow v under the condition mentioned above may be as shown. The angle of attack H can be seen to be a positive angle in this instance. The tail or horizontal tin load 174 under the proper design will always produce a reasonable load on the wire 148a and the positive angle H will be eliminated or at the worst not permitted to become positive enough to cause the lift on the hydrofoils 136:1 and 1361: to equal or exceed the weight 176 in water of the hydrostabilizer 132.

FIGURE 11 is a perspective view of a structurally simplified version of my invention. A three wire suspension system 180 is used to support hydrostabilizer 182. The three wire system 180 permits elimination of the mast 44 or the support bracket 148 used in the other versions of the invention, and has been found on test to be very effective in preventing the device from rolling over and breaking the surface of the water.

The cables or wires 180er, 180b and 180C are connected to attachments fixed directly to a constant chord, straight leading edge hydrofoil 184 which is preferably produced as an aluminum alloy extrusion. This leaves the central body 186 free from providing any part of the support system, and the body 186 then merely carries the loads from the horizontal iin 188 to the hydrofoil 184. The thin, elongated body 186 furnishes all the directional stabilization required, and a vertical iin is not needed at the tail of the hydrostabilizer 182.

The hydrofoil 184 has a rectangular planform with a span of 82 inches and a chord length of 12 inches, for example. The hydrofoil 184 has a symmetrical hydrofoil section throughout its span. The horizontal n 188 also has a rectangular planform with a span of 24 inches and a chord length of 6 inches. The horizontal fin 188 is preferably made of mahogany as is the body 186. The horizontal n has a generally rectangular hydrofoil section which is symmetrically tapered (sharpened) at its forward end portion throughout most of its span.

The wire 180a connects an attachment 198 fastened to the leading edge of the hydrofoil 184 on the longitudinal axis of the hydrostabilizer 182 to a hole 192 located near the forward end of an elongate support bar 194. The wires 180i) and 188C are similarly connected to respective attachments 196 and 198 on the hydrofoil 184 and the other ends of the wires 180]; and 180C are connected to a hole 208 located near the aft end of the support bar 194. The positions of the attachments 190, 196 and 198 are given by the dimensions I and I indicated in FIGURE 11. The dimension I is approxiamtely 9.9 inches and the dimension I is approximately 10 inches, for example.

The support bar 194 has connection links 202 and 204 which are adapted to be connected respectively to the ends of the wires 28661 and 206]] which correspond with the wires 34a and 34h shown in FIGURE 2. The wires 286:1 and 206!) pass over respective pulleys 46a and 461; mounted to the outer end 62 of the boom 28. The ange 64 is, of course, connected suitably to rope 38. Thus, the pitch of the support bar 194 can be varied by adjustment of the relative lengths of the wires 20611 and 206b. Adjustment of immersion depth of the hydrostabilizer 182 is also possible by varying the lengths of wires 206a and 28611 unreeled from the reels 48a and 481). It is, of course, possible to attach the upper ends of the wires 181m and 188i) and 180e directly to forward and aft points on the outer end 62 of the boom 28, and the depth of the hydrostabilizer 182 can be varied by raising or lowering the boom 28 on its inner pivot points. This would eliminate the need for the support bar 194, wires 206a and 20611, and the reels 48a and 48h.

FIGURES 12 and 13 illustrate the top plan view and side elevational View, respectively, of the hydrostabilizer 182. The body 186 is for example, approximately 251/2 inches long, 3% inchesd high and 11/2 inches wide. As can be seen in FIGURE l2, the widths of the forward and aft ends are tapered inwardly as shown. Similarly, as shown in FIGURE 13, the height of the aft end of the body 186 is also symmetrically tapered inwardly. The body 186 includes an upper forward portion 186a, a lower portion 186b and an upper aft portion 186C. These parts are shaped as indicated for proper mounting of the hydrofoil 184 and the horizontal iin 188 when assembled into the body 186. The hydrofoil 184 is set at an angle of incidence K of -5 degrees and the horizontal n 188 is set at an angle of incidence L of approximately 31/2 degrees, for example.

The upper forward portion 18611 of the body 186 is secured to the lower portion 186b by two wood screws 288. The upper aft portion 186C is similarly secured to the lower portion 186b by three wood screws 210 which also pass through a central portion 18801 of the horizontal iin 188 to secure it in position. The central portion 188e of tin 188 preferably is not tapered or sharpened -at its forward end portion as are the laterally extending sides thereof. The trailing edge of the horizontal iin 188 is located approximately 3 inches forward of the aft edge of the body 186, for example.

The lower surface and the upper surface of the front parts of the upper forward portion 186a and the lower portion 18611, respectively, are shaped to receive and accommodate the hydrofoil 184 as shown in FIGURE 13. The contacting surfaces of the hydrofoil 184 are set in epoxy and the hydrofoil 184 is secured in place by two bolts 212 which pass through suitable holes in the lower portion 18617, hydrofoil 184 and the upper forward portion 186g. Metallic plates 214a and 214b are set in transversely cut channels in the upper forward portion .186a and the lower portion 186b, respectively, of the body 186 to provide suitable engagement material for the bolts 212. The plates 214b are countersunk to accommodate the heads of the bolts 212 and the plates 214g are tapped to engage the threaded ends of the bolts 212. The weight of the hydrostabilizer 182 in air is yapproximately pounds and about 60 pounds in water.

The center of gravity of the device 182 in water lies on the arrow 21651 and on the arrow 216b in air.

Eyebolt 218 is threaded into a tapped hole 220 located in the leading edge at the center of the hydrofoil 184 as shown in FIGURES 12 and 13. The hole 220 has a countersunk forward portion to seat the base 218g of the eyebolt 218. Steel washers can be used as shims to seat the eyebolt 218 firmly in proper position as required. The attachment 196 for the wire 180]) (FIGURE l1) is shown secured to a countersunk =hole 222 (FIGURE 14) in the left side of the hydrofoil 184 in FIGURE 13. An eyeplate 224 is fastened to the hydrofoil 184 by screws 226 such that its upright center flange 224a extends up in the hole 222.

FIGURE 14 is a sectional view of the attachment 196 as taken along the line 14-14 indicated in FIGURE 13. Wire connection link 228 is rotatably attached to the center flange 224m on pin 230 and extends up beyond the upper surface of the hydrofoil 184. Since the hole 222 has an upper countersunk portion, the link 228 can pivot in a fore and aft direction to some extent 4as required. The attachment 198 on the right side of the hydrofoil 184 can, of course, be similar to the lattachment 196. A rotatable link which is suitably connected to the eyebolt 218 is also desirable for the attachment 190 for connection with the front wire 180a.

FIGURES 15 and 16 illustrate `a rotatable connection link which can be used with the eyebolt 218. FIGURE 15 is a fragmentary, side elevational view of the front end of the hydrofoil 184 with a connection link 232 rotatably secured to the eyebolt 218. FIGURE 16 is a view of the attachment 190 as taken along the line 16-16 indicated in FIGURE 15. The link 232 is rotatably connected to the eyebolt 218 by pin 234. Washers 236 can be provided as shown, and the pin 234 is secured in position by a lock pin 238. As will be apparent, the link 232 can be rotated on the pin 234 in a fore and aft direction a certain amount.

Another pin 240 similar to the pin 234 can be used to attach the wire 180:1 to the link 232. A connector lug on the end of wire 180a is engaged by the pin 240 between the end flanges 23201 of the link 232, and the pin 240 is secured in place by lock pin 242. Washers 244 can also be used as shown in FIGURES 15 and 16. Suitable connectors on the ends of the wires 180i) and 188C can be similarly attached t0 links (such as t-he link 228) of the attachments 196 and 198. Thus, the hydrostabilizer 182 will be suspended generally as indicated in FIGURE l1 when the wires 180o, 1881: and 188C are connected to their respective attachments 190, 196 and 198.

In operation, the hydrostabilizer 182 functions in the same manner as the other versions of hydrostabilizer. The operation described previously for the hydrostabilizer 132 is, of course, applicable for the hydrostabilizers 24 and'182. As mentioned before, the three wire suspension system was found to be particularly effective in preventing a hydrostabilizer from rolling over and breaking the surface of the water. However, a two wire suspension system especially when used with a suitable mast 44 or support bracket 140 which provides a raised rigid support, is entirely satisfactory and may in some cases be preferable. Such a raised rigid support is, of course, not absolutely necessary for satisfactory operation of the hyrostabilizer with a two Wire suspension system.

Operationally, where the boat 20 (FIGURES 1 and 2) suspends t-he hydrostabilizer 182 from the end of boom 28 on a three wire suspension system as shown in FIG- URE 11, and the boat 28 illustratively experiences a 20 degrees roll at a second rolling period for a boat speed of 91/2 knots, the angle of attack of the hydrofoil 184 with respect to the resultant water ow increases from the angle of incidence of approximately -5 degrees to about -20 degrees, for example, because of the vertical velocity component introduced in the relative water iow over the hydrofoil 184 due to its upward motion as caused by rolling of the boat 20. An increased angle of attack will, of course, result in a greater load or force on the hydrofoil 184 to suppress roll.

Since the boat 20 will usually roll isochronously, the angular roll velocity of the boat will decrease with rolls of smaller amplitudes at the 5 seconds rolling period. The vertical velocity component introduced by rolling is decreased and the angle of attack reduced. Thus, the loads on the hydrofoil 184 will be reduced with decreased amplitude of rolling of the boat 20. The resultant hydrodynamic loads on the 6 square foot hydro foil 184 for different angles of attack corresponding to different roll amplitudes experienced by the boat 20 at a 5 second period and -a speed of 91/2 knots are indicated in FIGURE 13 passing through the center of pressure position 246.

The generally harmonic roll motion of the boat 20 illustratively has a period of 5 seconds. For different roll amplitudes, the vertical travel of the hydrostabilizer 182 varies with the roll amplitude. The vertical distance traversed for the roll amplitude is covered in half the roll period, and the vertical velocity component due to roll at the midpoint of the roll .amplitude is directly proportional to amplitude of roll for the half roll period. The resultant velocity of relative water flow is, of course, the vector sum of the horizontal velocity component due to forward motion of the boat 2t) and the vertical velocity component due to roll.

The resultant loads are all shown intersecting the chord of hydrofoil 184 at the same point 246 for simplification. The center of pressure positions at the various ang-les o-f attack indicated actually are not `at one place on the chord line. They are close enough, however, to assume no differences for the purpose of illustration. The directions of the resultant loads or forces are, of course, those of the respective resultant vector sums of drag and (negative) lift loads on the hydrofoil 184 at the different angles of attack indicated in FIGURE 13.

Although the stabilizer system 22 is intended to be used primarily on `boats to stabilize the same, it can be readily adapted for use on other sea craft and the like. For example, hydrostabilizers laccording to my invention -suspended for respective pairs or sets of wires can be attached to suitable connectors provided on the wing tips of a seaplane to stabilize it while at anchor. Such use would, of course, be limited but can be beneficial and desirable under certain circumstances.

While some specific dimensions and types of material have lbeen given in connection with the exemplary embodiments of my invention described in the foregoing description, such specific dimensions and types of material are provided merely as examples only and are not intended to limit or restrict the scope of my invention. Similarly, it lis to be understood that the particular embodiments of my invention described above and shown in the drawings are merely illustrative of, and not restrictive on, my Abroad invention and that various changes in design, structure and arrangement may be made without departing from the spirit and scope of the lbroader of the appended claims.

I claim:

1. A suspended hydrofoil stabilizer system for stabilizing boats and. the like, comprising:

a pair of hydrostabilizers each having a center of gravity located on a longitudinal axis and adapted to be submersed in a fluid medium supporting a craft;

a pair of booms adapted to `be mounted to respective sides of the craft;

two sets of lines connecting said pair of hydrostabilizers respectively to said pair of booms, each set of lines including at least two lines connected to a corresponding hydrostabilizer at connection points located on normally vertical transverse planes which intersect the longitudinal axis at points respectively forward and aft of the center of gravity thereon; and

means for lowering and raising said hydrostabilizcrs in the fluid medium.

2. Apparatus as defined in claim 1 wherein each of said sets of lines are connected to a corresponding hydrostabilizer at connection points located at a predetermined distance above the longitudinal axis on normally vertical transverse planes which are longitudinally spaced `a predetermined distance apart, the normally vertical planes intersecting the longitudinal axis at points respectively forward and aft of the center of gravity thereon.

3. Apparatus as defined in claim 1 wherein said pair of hydrostabilizers each includes a body having a forward end and an aft end, a hydrofoil accurately attached to said @body toward said forward end, and a stabilizing fin assembly attached to said body near said a-ft end.

4. A suspended `hydrofoil stabilizer system for stabilizing boats and the like, comprising:

a pair of hydrostabilizers each having a center of gravity located on a longitudinal axis and adapted to be submersed in a fluid medium supporting a craft;

a pair of booms adapted to be mounted to respective sides of the craft;

two sets of lines connecting said pair of hydrostabilizers lrespectively to said pair of booms, each set of lines including at least three lines connected to a corresponding hydrosta-bilizer at connection points located on normally vertical transverse planes which intersect the longitudinal axis at points respectively forward and aft of the center of gravity thereon; and means for lowering and raising said hydrostabilizers in the fluid medium.

5. Apparatus as defined in claim 4 wherein said pair of hydrostabilizers each includes an elongate body having a yforward end and an aft end, a hydrofoil accurately attached to said body near said forward end, and a stabilizing fin attached to said body near said aft end.

6. Apparatus as defined in claim 5 wherein said lines on each of said sets of lines are connected respectively to at least three attachments which are adapted to be connected to points on said hydrofoil.

7. A suspended hydrofoil stabilizer system for stabilizing boats and the like, comprising:

a pair of hydrostabilizers each having a center of gravity located on a longitudinal axis and adapted to be submerged in a fluid medium supporting a boa-t;

a pair of booms adapted to be mounted to respective sides of the boat;

a pair of reeling means adapted to be mounted respectively to said pair of booms; and

two sets of wires connecting said pair of hydrostabilizers respectively to said pair of reeling means, each setv of wires including at least two wires connected to `a corresponding hydrostabilizer at connection .points located on normally vertical transverse planes which intersect the longitudinal axis at points respectively forward and aft of the center of gravity thereon.

8. Apparatus as defined in claim 7 including, in addition, means for indicating relative lengths of each of said wires of said sets of wire which have been unreeled respectively from each reeling means of said pair of reeling means.

9. A hydrostabilizer comprising:

a body having a forward end and an aft end, said body being relatively long and thin and having la longitudinal axis on which said hydrostabilizer has a center of gravity located;

a hydrofoil accurately attached to said body near said forward end, said hydrofoil being attached to said body at a negative angle of incidence .with respect to said longitudinal axis;

a stabilizing n assembly attached to said body near said aft end; and

at least two attachment means adapted to be connected to said hydrostabilizer to provide connection points for attaching at least two `suspension lines respectively thereto, said connection points being located on normally vertical transverse planes which intersect said longitudinal axis at points respectively forward and aft of the center of gravity thereon.

1t). Apparatus as defined in claim 9 wherein there are three of said attachment means for attaching three suspension lines respectively thereto, said three attachment means providing three connection points arranged in a predetermined pattern in which at least one point is located in a transverse plane forward of the center of gravity of said hydrostabilizer.

11. A suspended hydrofoil stabilizer system for stabilizing boats and the like, comprising:

a hydrostabilizer having a cen-ter of gravity located on a longitudinal axis and adapted to be submersed in a fluid medium supporting a craft;

a boom adapted to be mounted to one side of said craft;

:reeling means adapted t-o be mounted to the boom side of said craft; and

a set of lines connecting said hydrostabilizer to said reeling means, said set of lines including at least two lines connected to said hydrostabilizer at connection points located on normally vertical transverse planes which intersect the longitudinal axis at points respectively forward and aft of the center of gravity thereon.

12. Apparatus as defined in claim 11 including, in addition, means for indicating relative lengths of each of said lines of said set of lines which have been unreeled from said reeling means.

13. Apparatus las defined in claim 9 wherein said fin assembly includes vertical and horizontal stabilizing fins.

14. Apparatus as defined in claim 9, wherein said hydrofoil has symmetrical hydrofoil sections and is accurately lattached to said body to provide a planf'orm having a high aspect ratio, with sweepback and a constant taper ratio.

15. A hydrostabilizer comprising:

an elongate body having a forward end and aft end,

and having a longitudinal axis on which said hydrostabilizer has a center of gravity located;

a mast including a pair of longitudinally spaced means for connecting a pair of suspension lines respectively thereto, said mast being attached to said body towards said forward end and said connecting means providing connection points which are located on normally vertical transverse planes that intersect said longitudinal axis at points respectively forward and aft of the center of gravity thereon;

a hydrofoil accurately attached at a negative angle of incidence to said body toward said forward end; and

a stabilizing fin assembly attached to said body near said aft end.

16. Apparatus as defined in claim 15 wherein said fin assembly includes vertical and horizontal stabilizing fins.

17. Apparatus as defined in claim 15 wherein said body has a reference longitudinal axis and is relatively long and thin to provide a predetermined amount of directional stability to said hydrostabilizer, said hydrostabilizer having a center of gravity located on said longitudinal axis, and said means for connecting respective suspension wires to said mast and are located on normally vertical lines that intersect said longitudinal axis at points respectively forward and aft of the center of gravity thereon.

1S. Apparatus as defined in claim 17 wherein said hydrofoil has symmetrical hydrofoil sections and is accurately attached to said body to provide a planform having a high aspect ratio.

19. A hydrostabilizer comprising:

a body having a forward end and an aft end, said body having a longitudinal axis and is relatively long and thin to provide a predetermined amount of directional stability to said hydrostabilizer;

a hydrofoil accurately attached to said body near said forward end, said hydrofoil being attached to said body at a negative angle of incidence with respect to said longitudinal axis;

a stabilizing tin attached to said body near said aft end;

and

at least two attachments adapted to be connected to said hydrofoil to provide connection points for attaching at least .two suspension lines respectively thereto, said hydrostabilizer having a center of gravity located on said longitudinal axis and said connection points being located on normally vertical transverse planes which intersect the longitudinal axis at points respectively forward and aft of the center of gravity thereon.

20. Apparatus as dened in claim 19 wherein there are three of said attachments for attaching three suspension lines respectively thereto, said three attachments providing three connection points arranged in a predetermined pattern in which at least one point is located in a transstabilizer.

gravity of said hydro- References Cited by the Examiner UNITED STATES PATENTS 11/1915 Mustin.

10/ 1944 Chilowsky 244-137 X 7/1951 Seward 114-126 10/1961 Muldowney 114-235 6/ 1964 Brainard et al 114-235 FOREIGN PATENTS 5/ 1960 Norway.

15 MILTON BUCHLER, Primary Examiner.

T. M. BLIX, Assistant Examiner. 

1. A SUSPENDED HYDROFOIL STABILIZER SYSTEM FOR STABILIZING BOATS AND THE LIKE, COMPRISING: A PAIR OF HYDROSTABILIZERS EACH HAVING A CENTER OF GRAVITY LOCATED ON A LONGITUDINAL AXIS AND ADAPTED TO BE SUBMERGED IN A FLUID MEDIUM SUPPORTING A CRAFT; A PAIR OF BOOMS ADAPTED TO BE MOUNTED TO RESPECTIVE SIDES OF THE CRAFT; TWO SETS OF LINES CONNECTING SAID PAIR OF HYDROSTABILIZERS RESPECTIVELY TO SAID PAIR OF BOOMS, EACH SET OF LINES INCLUDING AT LEAST TWO LINES CONNECTED TO A CORRESPONDING HYDROSTABILIZER AT CONNECTION POINTS LOCATED ON NORMALLY VERTICAL TRANSVERSE PLANES WHICH INTERSECT THE LONGITUDINAL AXIS AT POINTS RESPECTIVELY FORWARD AND AFT OF THE CENTER OF GRAVITY THEREON; AND MEANS FOR LOWERING AND RAISING SAID HYDROSTABILIZERS IN THE FLUID MEDIUM. 